High frequency signal responsive control system



June 11, 1940. G BEERS 2,203,857

HIGH FREQUENCY SIGNAL RESPONSIVE CONTROL SYSTEM Filed larch 31, 1957 1 2 Sheets-Shet 1 George L. Beers FFEWE/VCY I (Ittorneg G. LQBEERS June 11, 1940.

2,203,857 HIGH FREQUENCY SIGNAL RESPONSIVE CONTROL SYSTEM Filed March 31, 1937 2 Sheets-Sheet 2 3rwentor 8 e rs George L. B

Gttorneg a as;

Patented June 11, 1940 ENT. OFFICE HIGH FREQUENCY SIGNAL RES PONS IVE f CONTROL SYSTEM George L}. Beers, Haddonfield, N. I L, as signor to Radio Corporation of America, a corporation of Delaware Application March 31, 19 3?, Serial No; 134,105

11 Claims. (c1. est- 20) 1 3 The present invention relates to a control system for radio receiving apparatus and thelike, andimore particularly to a control system responsiveto received signals or oscillations, to provide controlling potentials which may be applied to the circuitelements of a radio receiving system or the like in effecting control of, a predetermined portion, or a condition of operation of the system such as resonance indication, autoing, noise suppression or the like.

matic frequency or gainqcontrol, automatic tunto provide a control system of the character above referred to, which provides a. relatively large change in controljpotential for a relatively small change in the frequency of the applied signals or oscillations. a T l A further object of the present invention is to provide a control system for deriving a variable control potential, such as a biasing potential for radio tube circuits and the like, having a phase discriminating network in which a change in the,

Y frequency of applied signals or oscillations is converted into a difference in phase between two potentials normally having the same frequency.

It is also a further object of thepresent invention to provide a control system forradio receiving apparatus and the like, whichprovides a direct current control potential, the magnitude and polarity of which vary as the frequency of l the applied signalvaries from a predetermined primary and secondary of a conventional intervalue. n

It is also an object of the invention, to provide a control system which is adapted to derive a variable direct current biasing potentialjthe magnitude and polarity of which vary as the frequency of an applied signal varies from a predetermined value, and which maybe embodied in a radio receiving system in connection with existing circuits therein and without requiring the use of additional selective circuits.

It is also a furtherobject of thepresent invention, ;to provide a control system for radio tube circuits and the like in which a phase discrimi nating network is adapted to provide a variable direct current biasing potential in response to a difference in phase between two voltages having the same frequency. l

It is another object of the invention to utilize in any of the control systems above re ferred to,

a phase discriminatingnetwork which includes a pair of coupled tuned circuits, such as the mediate frequency transformer. V n

i It is an object also, of the presentinvention,

potential adapted to provide electrical indica tions Ofth direction in which one of said voltages is difiering fromthe other, in phase.

For the purpose of providing resonance indication and the like, it' is a still further object of the present invention to provide a control system responsive to phase differences between It is a primary objectof the present invention,

two signalsor oscillations havingthe same frequency, which provide an indication of one type atre so-nance, and an indication of another and of zero potential obtained at resonance.

The invention is also particularly adapted for use in connection with a superheterodyne type of radio receiver wherein the intermediate frequency amplifier provides coupled tuned circuits responsive to a predetermined intermediate free i quency; which coupled tuned circuits may readily be included in a phase discriminating network anda control system embodying the invention.

The invention will, however, be better under-- stood from the following description, when considered in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings: Figure 1 is aschematic circuit diagram of a control system embodying the invention.

Figure2 is a further schematic circuit diagram of radio receivingapparatus and the like, provided witha control system embodying the invention,

Figure 3 is also a schematic circuit diagram of tuned high frequency radio tube apparatus provided with a control system embodying the invention, said control system being a modification of that shown in Figure 1. i Figure 4 is a graph indicating the response elements I and 8, is provided as a preferred form of rectifier. The anode elements are connected to the opposite ends or terminals 9 and ID of a l tunedhighfrequency signal circuit II comprising a two-section inductance, indicated at l2 and I3, and a shunt variable tuning capacitor l4.

Two series connected resistor elements I5 and is are connected between the two sections of the ode t of the rectifier device.

The tuned circuit 20 comprises a second inductance or winding 2| and a shunt variable tuning capacitor 22 therefor. "The circuit 2D is preferably tunable throughthe same frequency range or to the same resonance frequencyas the circuit H. I I

The resistors l5 and iii are provided with bypass capacitors 23' and-24, respectively, and the terminals H and 18 are provided with output" leads 25 and 26, respectively, for applying control potentials derived from the resistors l5 and It, toany suitable control system in aradio receiver or like apparatus. :Theadaptability of the derived potentials for control purposes is indicatedin the following consideration of thecharaoteristics-of such potentials and operation of the. control network.

With-the control. network in a tuned signal circuit, if a voltmeter .or other voltage indication device 2 is connected between the control oroutput leads 25 and 26, and if the device is responsive to applied voltages toshow a deflection or indication in either direction from a centeror zero deflection, asshown, whereby it will indicate positive and negative polarities without reversal of the lead connections therewith, the

meteri 27 will show a zero deflection at resonance toean incoming-signal, adeflection in one direction for tuning adjustment below resonance to p nti 0 .1 he an des l and 8', as supplied y 'thetu-ned circuit H,,will be 180 out of phase.

The current. rectified by the section of the double diode including the anode l and the cathode 6 will flow from the anode 1 to the cathode 6 thence through the winding 2! of the tuned circuit 20, to the terminal l9, then through the resistor section it andthe inductance section [2, to the terminal 9 and the anode l. The current flowing through resistor 15 will be in such a direction to cause terminal H to become more negative with respect to the terminal l9. 1

The current rectified by the section of the double diode including the anode. 8 and the cathode will flow from the anode 8 to the cathodetthrough the winding 2! of the tuned circuit 26, to the terminal is, through the re sistor section it and the inductance section 13, to the terminal 2 and the anodeB. Thus it will be seen that a voltage induced in the tuned circuit M from any suitable source, will cause ,a currcntto: flow through the resistor It in such. a direction to make the tc-irminal |8 more negative with respect to the terminal ii), in the samernanner that the terminal i1, ,is made more negative than the terminal I9. I I

Thus, if the inductance sections are equal, equal radio frequency voltages will bedeveloped thereacross and, the voltages developed across resistors 15 and i idue to the rectified current flowing therethrough will be equal and opposite inpolarity, if the resistors i5 and H5 have equal resistance values. Therefore, a'voltage induced into the tuned circuit M will not cause a difference of potential to exist between the resistor output terminals 5? and i8. I

If a voltage is induced only into the tuned circuit 29, it will be seen that it'will be applied to the'anode elements 1 and 8 in phase, This voltage will likewise cause equal rectified currents tOflOW through resistors I5 and; and in opposite'directions iromthe center terminal 19, such that the voltages developed across the resistors are in opposition'and that again, no difference in potential will exist between the terminals I! and i8.

' Therefore, if asignal or high frequency voltage is applied to the diode rectifier by the tuned, circuit H, the difierential potential or net voltage developed across the outputterminalsl'l and It will be substantially zero; The same condition is provided if a signal or high frequency voltage isapplied to-the diode-rectifier elements throug only the tuned circuit 20.

I Assuming-new, that .a high frequency signal is supplied to'the dioderectifier through both tuned circuits and the. voltage applied to the anode ele-' add and a large current will flow-through the resistor, I5. The'voltages on the anode 3 connected tothe terminal l0 are then out of phase and if theyare equal these voltages will cancel and nocurrent will :fiow through the resistor H5. The, difie'rential -voltage then appearing across the resistor combination l5 and H5 at the output leads 25 and 26 or the terminals H and i8 will be such that the terminal i! will be negative with respect to-terminaLtB. If the terminal I9 is connected to ground as indicated at 2B, the lead 25 will be negative with respect to ground while the lead 26 will be substantially at ground potential.

If the phase of the voltagesupplied to either tuned circuit is now shifted bylBO, the large current will ,ilowthrough the resistor Hi. In this case, the voltage appearing across the outputv terminals ;I1 and I8 and :the leads 25 and 26 will be such that the terminal l8 will be negative,

with respect to. the, terminal 11. u

If the phase of thevoltage obtained from the tuned circuit 2i! differs by 90 from that supplied by thetuned circuit H the current flowing through theoutput resistor IE will be equal and opposite to that flowing in the output resistor l5 and no voltage will be obtainedat the ter minals l7 and I8 orthe output leads 25 and 26.

Thusit will beseen that. as thephase difier encein thevoltages supplied by the tuned cir-v term will notonlyindicate resonance, but will also indicate on which side of resonance the applied signal is tuned as the tuning is varied. Thus it has been, shown that by employing a phase discriminatingnetwork such as that illus-' trated inFig. 1, a control potential can be de: rivedwhich ,varies both inmagnitude and polarity with that impressed on the anode 43 from the. tuned secondary circuit, which includes the secrelation between two signal voltages.

For example, I have found that if a received signal is passed through two portions of a receiving system, one of which has a selectivity characteristic such as illustrated by curve ABC in Fig. .4, and the other of which has a selectivity characteristic represented by curve )DBE in the same figure, that the phase relation between thetwo voltages representing the signal output of these twoportions of the receiving system, will vary through approximately 180 as the frequency of the applied signal is varied. If the signal voltage applied to the input circuits of the twoportions of the receiver are in phase and if the difference in thenumber of coupled tuned circuit amplifier stages in the two portions of the receiver is anodd number, then the output voltages of the two signal channels will be 98 out of phase at resonance. i

This arrangement will best be understood by reference to Fig. 2 of the drawings, wherein the rectangle .38 represents any suitable radio receiving system having tuningwmeans indicated by the tuned circuit 32 and variable tuning ca- 1 pacitor 33, and means provided by an input windcuit for the receiving system is indicated at 35 and includes a coupling transformer having a tuned primary winding 31 coupled to a secondary winding comprising two substantially equal inand 64, 85.

connected in the plate circuit of tube 68.

ductance sections 38 and 39. The secondary sections are connected in series at their inner or adjacent ends through two resistors 48 and 4|,

and at the opposite orouter ends are connected with a shunt tuning capacitor 42 and the anode electrodes 43 and 44 of, a double diode rectifier 49, the common cathode of which isindicated at The resistors 48 and 4| are provided with shunt bypass capacitors 46 and 41, and the center tap to the cathode 45 throu gh. a tuned secondary winding. 58 .of a second coupling transformer 54. The transformerf54 is provided with a tuned primary winding which is connected to a suitable two-way switch having movable contact elementstn and GI, and. fixed contacts 62, 63,

. The grid of an amplifier tube 68 is coupled to the anode end of the inductance 38 by means of a coupling capacitor 66. G-Yrid bias potential is provided through a resistor Bland a self bias resistor 69. The anode of this tube is connected to the switchcontact83. When theswitch elements 68 and 6| are connected with the contacts 63 and 65, the tuned primary which includes the inductance 5| and the variable capacitor 53, is

Signal potential appearing across the tuned circuit,

impressed on theanodes43 and 44, 180 out of phase, and on the grid of tube 88, in phase with the potential on the anode 43. The signal output of the tube 68 is impressed on the anodes 43 and 44 of the double diode rectifier 48 through l the coupled tuned circuit transformer 54. Since ondary inductances 38 and 39 ofthe transformer 38, the voltage developed across the secondary 58 of the transformer 54,is 98 out of phase with the voltage across the secondary of transformer quency of the transformers 36 and 54, causes two voltages at the, same frequency to be applied to the double diode 45,;one of which voltages is 90 out of phasewith the other. cy of thereceived signal is variedslightly, or if the tuning of the receiver is varied slightly, the phase relation between'the two voltages will vary through a range ofapproximately 180. As this change in the phase relation between the two voltages occurs, the voltage across resistors 48 and 4| will vary in the manner previously described. i

Thus the voltage across this resistor combination will decrease from a given negative value, pass through zero, and then increase until it reaches a positive value comparable to the initial negative value as the receiver is tuned from one side of the receiver resonance characteristic to the other. r

This same variation in the potential developed across the resistor combination 48-4| will occur if a signal from a local oscillator, illustrated and 6| to the contacts (and 64 respectively.

.Thus, if the oscillator 52 is arranged to provide will be out of phase with the signal on the anode 44. Under this condition, the maximum current will fiowthrough resistor 48 and no current will flow through resistor 4|. If the received signal potential is reversed in phase by 180, then a current will flow through resistor 4| and no current will flow through resistor 48.

If the phase difference between the received signal and the local oscillator potential on the anode of the double diode rectifier is 90 then equal currents will flow in resistors48 and 4|.

Since these currents flow in opposite directions from the anode connection at the terminal 48, by reason of the rectifier action, the voltage at the outerend terminals 55 and 58 of the resistor combination will be zero, since the total voltagedrop across the two resistors will be zero.

Thus, the direction and magnitude of the voltage developed across the resistor combination 48 and, connected inthe center of the secondary winding, is a function of the phase relation between the received signal or intermediate frequency voltage and the local oscillator voltage provided by the source 52. The receiver circuits are so arranged that when the receiver is tuned to resonance, the carrier wave or intermediate frequency signal as applied to the rectifier 43, is 98 out of phase with the oscillator voltage; whereby the direct current biasing potentials across terminals 55 and 56 are zero.

The direct current control or bias potential developed across the resistor combination 48-4-| may then vary in either direction in accordance with variation of the tuning from resonance, and the potential developed at the terminals "55 As the frequen- .by the block 52 is applied to the transformer 58 by connecting the switch contact members 68 control leads 51.

and'56 maybe utilized to control the tube cir' cuits of the receiver 30 in. any suitable manner.

As the frequency ofthe received signal tends to vary from. that provided bythe oscillator, the

phase shift caused thereby disturbs the balance in potential drop between the resistors 49 and M,

and a: corresponding change in bias or'co ntrol' potential at the terminals 55 and 56'may be appliedto the receiving system 30 through suitable Another modification. which I have found to be very satisfactory for'applying the twoalternating current voltages to the phase discriminating. network is to make use of the voltage across both the primary and secondary of acoupled tuned circuit transformer.

Referring to Fig. 3, a portion of anintermediate frequency amplifier circuit is shown, comprising an intermediate frequency amplifier tube con- :nected with an intermediate frequency input transformer H and having an output circuit 12' coupled to the primary winding 13 of a second intermediate frequency coupling transformer 36a. The secondary is divided into two equal winding sections 14 and 15, whereby it is adapted to be connected into a phase discriminating network of the type shown in the preceding figures, for

deriving control potentials through a diode rectifier device H5.

In this circuit, however, the diode rectifier anodes, indicated at T1 and 18, are connected with the end terminals of the secondary which istuned by a suitable shunt tuning capacitor 19, but'the potential applied between the cathode indicated: 1 at 80, and the center tap 8| of the output resistors 82 and 83 is derived from the high potential ter-.'

minal 84 of the primary or input circuit. 815, the connection being made between the cathode 80 and the high potential terminal 84 through a lead 86. The opposite side of the tuned primary 'winding is connected to ground as indicated at 81. Likewise the center tap BI is connected to ground as indicated at 88. Direct current. control potentials are derived from the resistor output terminals 89 and 90 through output leads indicated at 9! and '92.

In this circuit, advantage is taken of the fact that at resonance the primary and secondary voltages, of the coupled tuned circuit intermediate frequency transformer. 36a, are 90 out of phase with each other. By applyingv the voltage across the primary of the transformer between the oath-- ode 86 and the resistor center tap 8i, and the secondary voltage betweenthe two diodeanodes l1 and 7B, the desired phase relations for the phase discriminating network are obtained. If

Til-I the frequency of the signal applied to the transformer is changed either because of a slight change in the tuning of the receiver, or a change in the frequency of the transmitter, the phase relation between the primary and secondary volt ages will change. mately 180? will be obtained betweenthe primary and secondary voltages as the frequency of the signal applied to the transformer is varied through the frequency range included within. the resonance characteristic of the transformer 3611.

When the signal applied to the intermediate frequency amplier tube 16 is in resonance with the transformer feeding the double diode rectifier 16, a voltage will be applied between thev cathode 80 and the resistor center tap 81 which will be 90 out of phase with the voltagedeveloped across the secondary coil sections 14 and T5 and appliedbetween the anodes TI and 18.

A phase change of approxi 9!! will be zeros Likewise if only the voltage de:-

veloped across the secondary of the transformer is applied to the double diode rectifier between the anodes Tl and 18, the rectified current flowing through the resistor section 82 will be equal andopposite in direction'to that flowing through w sistor section83 and. the voltage'between the terminals 89 and 90 will be zero.

-If both the primary and secondary voltagesare applied to the double diode and these voltages are 90 out of phase, as will be obtained if the signal applied to the transformer has the frequency to which the transformer is resonant, then the signal voltages applied to the two anodes will still be equaland the rectified currents flowing through the two resistor sections will be equal and opposite and the voltage between terminals 39 and 99 will be zero.

If, however, the signal potential applied .to the transformer has a frequency which differs slightly from the resonance frequency of the transformer, the phase relation between the primary and secondary voltages will no longer be 90 and the sig nal. potentials applied to the two anodes will not be equal and a difference in potential will exist between the terminals 89 and 90 because the rectified-currents flowing through resistor sections 82 and 83 will be unequal.

. Let us assume for example that the applied signal has a frequency which isjust inside the frequency response characteristic of the transformer. With. a conventional intermediate frequency transformer this signal frequency would differ from the resonance frequency of the transformer by from 2 .k. c. to 5 k. 0. Under these conditions a phase difference of approximately 180 would exist between the primary and, secondary voltage.

Let us assume that with this phase difference, the. voltages are suchthat the voltage applied to the anode H by the primary of the transformer is in phase with the voltage applied to this anode by the secondary of the transformer. The voltages applied to this anode will then. add and if they are'equal the-anode signal potential will then be twice the value obtained when only the secondary voltage is applied to the double diode. This will cause a corresponding increase in the rectified current flowing through resistor 32. On theother hand the signal potentials applied to the anodeflli will be 180 out of phase and if they are equal in magnitude, the sum of the voltages on this anode will be zero. Therefore, no current will flow through resistor 83 and consequently no drop in potential will occur across this resistor.

Since considerable current flows through resister 82, a relatively large voltage will be developed. across this resistor and this voltage will appear between the terminals 89 and 90. Since the current causing this drop in potential must flow through the circuit comprising the resistor 82 and the anode l"! and cathode 83, the direction of the current will be such that the terminal 8 9 will be negative with respect to terminal 90.

'If the frequency of the signal applied to the transformer feeding the double diode is changed so that it just falls within the other side of the transformer frequency response characteristic, 1i

thewfrequency.ofisaidtpotentials to change said the phase relation between;v the primary. and secondary voltages will shift by approximately: 180

Under this condition, the large signalpotential ,will be applied to the anode 18 while thesignal potential on the anode 'l'll will be substantially zeros Considerable rectified current will now flow through resistor 83 and .no current will flow through resistor. 82. This currentwill fiow through resistor 83 in such a direction thatthe resultant dropoin potential acrossthis resistor causes the terminal 89. to become positive with respect to theterminal. 90. i K

i Thus, as the. frequency of the signalbapplied to the transformer is varied. throughthe frequency range corresponding. to the transformers frequency response characteristic the potential across the terminals 89 and 90 will decrease from a given value, pass through zero, change polarity, and increase to the initial. .value again. This change in potential across terminals 89 and 90 as. the frequency of the signal applied to the transformer is varied may bennderstood more clearly by reference to Fig.-5.. lnuthis figure the curve I0! is the frequency responsescharacteristic of the coupled tuned circuit transformer used to feed the double diode rectifier. The curve designated M6, 102,104, I08 shows the variation in the voltage between terminals 19 and 80 as the frequency of the applied signal is varied across the frequency response characteristics of the transformer. The large change in! control potentialmade available for a small change in frequency is quiteiapparentfrom this curve. As previously stated, this control potential can beutilized in any desired manner. 1

.From theforegoing description, it will be obvious that in a control system which employs a phase discriminating. network as shown, a

change in either the frequency of a received signal lor .a change in; the. tuningof the receiver,

is converted into a difference in phase between two voltages which arethen applied to-lthe phase discriminating1 network. By utilizing. the vol-.

tages .Whichmay appear. across the primaryand secondary of a coupled tuned circuit transformer, I have provided in one embodiment of my invention, a simple arrangement for converting afchange in-tuningfrom resonance, or a change inthe frequencyof a received signal,g.into a change in, the phase relationzbetweentwo alternating current voltages ,havingthe samefre quency. I have likewise disclosed means for deriving control potentials from said changein phase relation.

While the inventionyhas been and described as applied to radio signal receiving circuits, it should be understood that this is for purposes of illustration and should not be taken as a limitation in the application thereof to' other circuits. for control purposes in response to applied signals.

For example, I contemplate other uses, including the control of circuits operating at frequencies as used in power circuits, at audio frequencies, in synchronizing generators for television and the like, as Well as for other purposes hereinbefore mentioned.

.I claim as my invention:

1. A signal responsive control system comprising in. combination, means including two signal conveying circuits in cascade tuned to resonance atthe same frequency and providing two signal potentials having at all times the same frequency and a predeterminednormal phase relation, said means. being thereby responsive to a change in verting a variation in frequency of said received signal into a variation in phase between said potentials,,,said first and second named means including the primary and secondary of a coupled tuned circuit transformer through which said received signal is conveyed-means. for converting avariation in phase between said potentialsinto a controlling potential, said means including a double diode rectifier ,device having a pair of anodes one connectedwith each of the terminals of the said secondary, a cathode connected through said primary with the secondary,

and a resistor network in the secondary providing a center tap for said last named connection, and a control circuit for said system connected with saidyresistor network to derive said controlling potential therefrom. l

q 3. Ina signalling system, the combination of a tunable signal circuit,,means for derivingtwov signal potentials from said circuit in response to an applied signal, means forconverting: a

change in the frequency of the applied signal into a change in phase between said signal po-. tentials,said first and, second named means including a pair of tuned interstage coupling cin circuits arranged incascade in said system, and

connectedwith said signal. circuit, means; con-,

nected with said circuits for. deriving. a -controlling potential therefrom responsive to Said change in phasebetween said signal potentials, and means, for

v applyingat least a portion of said controlling control a condition ofoperation thereof.

4. In a high frequency signal control system, the combination of means providing a signal source tunable to a, predetermined frequency, at least two resonant clireuitspoupled to f each other and arranged incascade, the first offsaidI circuits. being coupled to said signal source to receive energy therefrom, eachof said resonant circuits being tuned to the same predetermined frequency, whereby, at resonance, potentials across saidcircuits difiering90 in. phase are provided, and control means responsive to a .phase angle change between said potentials when a signal from the source tends to depart from resonance with said coupled circuits,

5. In a signaling system, the combination of means providing a signal source tunable to a predetermined frequency, a frequency variation response network coupled thereto, including two signal circuits in cascade tuned to the .same predetermined frequency and so coupled in the system that apredeterminedphase angle exists potential to. said systemi to between potentials established therein in respouse to an appliedsignal, means for applying an input signal to the first of said signal circuits, said network being responsive to variations in the tuning response of said system and variations in the frequency of an applied signal to cause a change in the phase angle between said potentials, means for rectifying, said poten-. tials, and means for deriving from said rectifyi I the frequency of an applied signal above and ing meansa differentialcontrolling potential for g said system. l

6. A'high frequencycontrol system comprising in combination, a frequency discriminating .net-

, work comprising primary and secondary resonant circuits tuned to a common operating frequency, said primary and secondary circuits being so. re-

lated that vector sumpotentials of the primary and secondary voltages are provided, said potentials varying" in magnitude with variations in below the common resonant frequency of said primary and secondary circuits, rectifier means connected with said primary and secondary circuits for rectifying said sum potentials, and means for deriving direct current potentials therefrom which add in opposition at resonance to provide a substantially zero controlling potential and havinga polarity and magnitude" above I signal from the resonancefrequency of said I and below resonance dependent upon the direction and degree of departure of an applied circuits '7. A high frequency' control system comprising in combination, means providing two tuned cou-' p led high frequency signal circuits, one of said circuits providing a divided secondary winding having, two sections, outputrresistor means connected between said sections and having a center tap thereon, diode rectifier means having a pair of-anodes- "connected with the terminals of said last named circuit and having a cathode connected to said center .tap, said cathode being coupled to the other of said circuits and the relation of said circuits being such that direct current voltages introduced by said 'tunedci-rcults through said resistor elements have a phase difference of substantially 1at the resonance frequency of said circuits, means for tuning said circuits tosaidresonan-ce frequency, and means for deriving a control potential from" the termi- "na'ls of the output resistormeans;

' 8; In a superheterodyne receiver, the combination with tuning means therefor, of an intermediate: frequency amplifier, a coupling trans former for said amplifier having a primary winding and a secondary Winding, said secondary winding having two sections, a resistor element having a center tap connected between. said sec- ,am'tions, a rectifier device'having a cathode and two anode electrodes associated therewith, said anode electrodes being connected with the terminals of said secondary winding and'said'cathode being coupled to the primary winding and conductively connected withsaid'center tap,and

potential from said network which varies in powlarity and magnitude with the difference in phase between the potentials existing in said two resonant circuits, and means for applying said controlling: potential tov the system to control a condition of operation thereof.

10. In combination, a. source of electric waves of a predetermined operating frequency, at least two resonant circuits coupled to each other and arranged in cascade, the first of said circuits being coupled 'tosaid wave source to receive waves therefrom, each of said resonant circuits being tuned to the said operating frequency, the

potentials across said coupled resonant circuits differing 90 in phase when the waves impressed thereon are of the said operating frequency, and means-responsive to a phase angle change between. said potentials when the applied waves depart from resonance with said coupled circuits to provide a differential control potential which varies, in magnitude and polarity with degree of departure from and on either side of resonance.

11. In a radio receiving; system, tuning indication means therefor comprising in. combination', an intermediate frequencyamplifier coupling transformer, means for tuning the primary and secondary of said transformer to the same intermediate frequency; a phase discriminating network including said tuned primary and sec-,- ondary circuits for deriving a directcurrent controlling potential therefrom which varies inacr co'rd'ance with variations of a received signal from the resonance frequency of said tuned coupled circuits, and means in said network, responsive to the difference in phase between the primary and secondary voltages for producing a-differential direct current potential having a magnitude and polarlty determined by saidphase difference, and a polarized indicating" means responsive-"to said differential potential. r

GEORGE L. IBEER SL 

